Beta releases are backwards-compatible with stable releases - I think you are asking to make stable releases forwards-compatible with future beta releases.
In general this is not really possible, since we can't predict the future. For example if we add a new feature in a beta release (such as the new functions feature), the previous stable release can't know how to open projects using that feature. It can be difficult even to ignore unknown parts of the project, since everything tends to consist of a great deal of cross-references, and it would complicate verifying that the project file is actually valid (since it can't really tell the difference between an invalid/corrupt project, and a project file from the future).